1. Field of the Invention
The present invention relates to a high-intensity magnetic separator operating in a humid environment for separating magnetic particles from a fluid material containing such particles, for example a liquid or a pulp containing the magnetic particles in suspension. Magnetic separators of this type comprise at least one vertically extending housing having side walls defining a separating chamber and means for generating a magnetic field extending perpendicularly to the direction of circulation of the fluid material in the separating chamber. The separating chamber may contain a ferromagnetic matrix permeable to the fluid material, such as an array of grooved plates, balls, expanded metal elements, iron scale or the like, to enable the fluid material to circulate through the matrix in the chamber.
2. Description of the Prior Art
The conventional magnetic separators may handle discontinuous batches of fluid material and are operated cyclically, i.e. in a separating phase the fluid material is circulated through the separating chamber while a magnetic field is applied thereto, the magnetic constituents contained in the material are retained on the housing walls and/or on the ferromagnetic matrix in the chamber, and the non-magnetic constituents are entrained by the liquid of the material and are collected; and in a subsequent washing phase the circulation of the fluid material is stopped, the magnetic field is removed, and the retained magnetic constituents are evacuated from the chamber by means of a washing liquid, usually water, circulated through the chamber under pressure. Usually, electromagnets are used for generating the magnetic field so that the same may be demagnetized readily to remove the magnetic field during the washing phase.
It has also been proposed to use permanent magnets in magnetic filters for purifying liquids charged with small amounts of magnetic particles and not requiring frequent cleaning. In such filters, the separating chamber is constituted by a replaceable casing which can be exchanged for a new one after the magnets have been detached. This type of filter cannot be used for treating materials containing substantial amounts of magnetic particles.
Continuously operating magnetic separators comprise a plurality of separating chambers arrayed in a ring or an endless chain, and the separating chambers are continuously displaced relative to fixed magnetic pole pieces arranged perpendicularly. During their continuous displacement, the separating chambers pass successively through a zone of separation, a zone of rinsing and a zone of evacuation of the magnetic particles. The fluid material is fed to the chambers in the zone of separation substantially along the entire length thereof. At the end of the separation zone, where the magnetic field is still intense, a rinsing liquid is circulated through the chambers to eliminate the non-magnetic grains of the material retained by magnetic floculation. In the evacuation zone, where the magnetic field is substantially zero, the magnetic particles are evacuated by a washing liquid fed to the chambers under pressure. These continuous action separators are heavy and cumbersome, and they are accordingly very expensive. Since they operate with electromagnets, they consume a considerable amount of electric energy.
While the literature has proposed replacing the electromagnets by permanent magnets in such separators, this has never been done in industrial applications because the intensity of the magnetic field obtainable with permanent magnets is limited in such an apparatus, due to the spacing required between the walls of the separating chambers and the magnets to permit the displacement of the chambers relative to the magnets.